Supernovae ( SNe ) have been proposed to be the main production sites of dust grains in the Universe .
Our knowledge on their importance to dust production is , however , limited by observationally poor constraints on the nature and amount of dust particles produced by individual SNe .
In this paper , we present a spectrum covering optical through near-Infrared ( NIR ) light of the luminous Type IIn supernova ( SN IIn ) 2010jl around one and half years after the explosion .
This unique data set reveals multiple signatures of newly formed dust particles .
The NIR portion of the spectrum provides a rare example where thermal emission from newly formed hot dust grains is clearly detected .
We determine the main population of the dust species to be carbon grains at a temperature of \sim 1 , 350 - 1 , 450 K at this epoch .
The mass of the dust grains is derived to be \sim ( 7.5 - 8.5 ) \times 10 ^ { -4 } M _ { \odot } .
Hydrogen emission lines show wavelength-dependent absorption , which provides a good estimate on the typical size of the newly formed dust grains ( \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ < $ } } 0.1 \micron , and most likely \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ < $ } } 0.01 \micron ) .
We attribute the dust grains to have been formed in a dense cooling shell as a result of a strong SN-circumstellar media ( CSM ) interaction .
The dust grains occupy \sim 10 % of the emitting volume , suggesting an inhomogeneous , clumpy structure .
The average CSM density is required to be \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ > $ } } 3 % \times 10 ^ { 7 } cm ^ { -3 } , corresponding to a mass loss rate of \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ > $ } } 0.02 M% _ { \odot } yr ^ { -1 } ( for a mass loss wind velocity of \sim 100 km s ^ { -1 } ) .
This strongly supports a scenario that SN 2010jl and probably other luminous SNe IIn are powered by strong interactions within very dense CSM , perhaps created by Luminous Blue Variable ( LBV ) -like eruptions within the last century before the explosion .